The present invention relates to a gas turbine engine having an active clearance control system to maintain clearance between rotating blades and seals in a stationary casing of the gas turbine engine.
In a gas turbine engine, hot combustion gases flow through an annular gas passage between a rotor and a casing of the turbine engine. Rotating blades, e.g., buckets, extend radially from the rotor and into the annular gas passage. The hot combustion gases flowing over the blades rotate the turbine and thereby drive the gas turbine.
There is a gap between the tips of the rotating blades and seals the casing. Because the gap is small, there is a risk that the tips of the blades can impact, or rub against the seals. This risk of rubbing is increased as the gas turbine engine heats during startup and rapid throttle movements, and cools during rapid decelerations and shutdown. The thermal expansion rates of the casing and seals tend to be different than the thermal expansion rates of the turbine rotor and the blades. These differences may cause variations in the clearance between the tips of the blades and the seals. For example thermal expansion of the rotor and blades may cause the blade tips to approach the casing, before the casing expands to accommodate the changes. If the clearance were to become too small, the blade tips can impact or rub against the seals of the casing.